The present invention relates to the recording, storage and reading of magnetic data, particularly rotatable magnetic recording media, such as thin film magnetic disks having textured surfaces for contact with cooperating magnetic transducer heads. The invention has particular applicability to high areal density magnetic recording media designed for drive programs having a reduced flying height and improve shock resistance for mobile computer data storage applications.
Thin film magnetic recording disks and disk drives are conventionally employed for storing large amounts of data in magnetizable form. Typically, one or more disks are rotated on a central axis in combination with data transducer heads. In operation, a typical contact start/stop (CSS) method commences when the head begins to slide against the surface of the disk as the disk begins to rotate. Upon reaching a predetermined high rotational speed, the head floats in air at a predetermined distance from the surface of the disk due to dynamic pressure effects caused by air flow generated between the sliding surface of the head and the disk. During reading and recording operations, the transducer head is maintained at a controlled distance from the recording surface, supported on a bearing of air as the disk rotates, such that the head can be freely moved in both the circumferential and radial directions allowing data to be recorded on and retrieved from the surface of the disk at a desired position. Upon terminating operation of the disk drive, the rotational speed of the disk decreases and the head again begins to slide against the surface of the disk and eventually stops in contact with and pressing against a landing zone of the disk. Thus, the transducer head contacts the recording surface whenever the disk is stationary, accelerated from the stop and during deceleration just prior to completely stopping. Each time the head and disk assembly is driven, the sliding surface of the head repeats the cyclic operation consisting of stopping, sliding against the surface of the disk, floating in the air, sliding against the surface of the disk landing zone and stopping.
It is considered desirable during reading and recording operations to maintain each transducer head as close to its associated recording surface as possible, i.e., to minimize the flying height of the head. Thus, a smooth recording surface is preferred, as well as a smooth opposing surface of the associated transducer head, thereby permitting the head and the disk to be positioned in close proximity with an attendant increase in predictability and consistent behavior of the air bearing supporting the head. However, if the head surface and the recording surface are too flat, the precision match of these surfaces gives rise to excessive stiction and friction during the start up and stopping phases, thereby causing wear to the head and recording surfaces eventually leading to what is referred to as a xe2x80x9chead crash.xe2x80x9d Thus, there are competing goals of reduced head/disk friction and minimum transducer flying height.
Conventional practices for addressing these apparent competing objectives involve providing a magnetic disk with a roughened recording surface to reduce the head/disk friction by techniques generally referred to as xe2x80x9ctexturing.xe2x80x9d Conventional texturing techniques involve polishing the surface of a disk substrate to provide a texture thereon prior to subsequent deposition of layers, such as an underlayer, a magnetic layer, a protective overcoat, and a lubricant topcoat, wherein the textured surface on the substrate is intended to be substantially replicated in the subsequently deposited layers.
The escalating requirements for high areal recording density impose increasingly greater requirements on thin film magnetic media in terms of coercivity, stiction squareness, low medium noise and narrow track recording performance. In addition, increasingly high density and large-capacity magnetic disks require increasingly smaller flying heights, i.e., the distance by which the head floats above the surface of the disk in the CSS drive. The requirement to further reduce the flying height of the head renders it particularly difficult to satisfy the requirements for controlled texturing to avoid head crash.
Conventional laser texturing techniques have previously been applied to metal-containing substrates or substrates having a metal-containing surface, such as Nixe2x80x94P plated Al or Al-base alloys. Such substrates, however, exhibit a tendency toward corrosion and are relatively fragile, thereby limiting their utility so that they are not particularly desirable for use in mobile computer data storage applications, such as laptop computers. Glasses and glass-ceramics, i.e., two-phase materials comprising an amorphous glass phase and a crystalline ceramic phase, exhibit superior xe2x80x9chardnessxe2x80x9d, resistance to shock, heat resistance and chemical stability (acid and alkali resistance) than Nixe2x80x94P plated Al or Al-alloy substrates. Accordingly, glass and glass-ceramic substrates are capable of being polished to a greater smoothness than Nixe2x80x94P plated Al or Al-alloy substrates for high areal density ultra-low flying height application and provide better shock resistance for use in mobile computer data storage application. However, it is extremely difficult to provide an adequate texture on a glass or a glass-ceramic substrate, particularly in view of the escalating requirements for high areal recording density.
Conventional practices for texturing a glass or glass-ceramic substrate comprise heat treatment during which the crystallization temperature is maintained for about 1 to about 5 hours to generate secondary crystal grains forming the surface texture characterized by irregular protrusions with surrounding valleys extending into substrate.
The use of heat treatment to form a textured surface on alternate substrates, such as glass or glass-ceramic substrates, is undesirably slow and inefficient in terms of energy consumption. Significantly, it is extremely difficult to exercise control over the size and shape of the secondary crystal grains due to inherent limitations in controlling temperature uniformity. Accordingly it is virtually impossible to provide a glass or glass-ceramic substrate with a controlled textured landing zone for optimizing flying height and maximizing data zone recording density. Moreover, the resulting texture comprises irregularly shaped protrusions with surrounding valleys extending into the substrate, thereby creating undesirable stress profiles during subsequent deposition of layers by sputtering at elevated temperatures. Such undesirable stress, profiles render it extremely difficult to accurately replicate the texture in subsequently deposited layers. It is also difficult to optimize both the bulk and surface properties at the same time because the entire substrate is heated. In addition, it is not possible to provide a glass-ceramic substrate with a controlled textured landing zone together with a super-smooth data zone to maximize recording density.
Pulsed laser light beams have also been employed to laser texture substrates, such as glass-ceramic substrates. Kuo et al. in U.S. Pat. No. 5,853,820 disclose a method of manufacturing a magnetic recording medium comprising texturing a surface of a glass-ceramic substrate with a pulsed, focused laser light beam to form a plurality of protrusions, wherein the crystalline phase of the glass-ceramic substrate is less than about 70% by volume. Kuo in U.S. Pat. No. 5,714,207 discloses a method of manufacturing a magnetic recording medium comprising texturing a surface of a glass or glass-ceramic substrate with a pulsed, focused laser light beam to form a plurality of protrusions and controlling the height of the protrusions by controlling the quench rate during resolidification of the laser formed protrusions. Xuan in U.S. Pat. No. 5,955,154 discloses a method of manufacturing a magnetic recording medium by comprising laser texturing an upper surface of a glass-ceramic substrate with a pulsed, focused laser light beam to form a textured upper surface by localized crystallization.
Such techniques for laser texturing glass or glass-ceramic substrates employ a pulsed focused laser light beam, typically at a wavelength of about 10.6 gm from a carbon dioxide (CO2) laser source. The textured glass or glass-ceramic substrate comprises a two-dimensional array of discrete dome-shaped bumps or protrusions extending about the substrate surface. The laser textured landing zone provides a head-bump-interface to alleviate the head-disk stiction. The bump height is controlled by adjusting the laser pulse width and laser power. Typically, the bump height extends above 50 xc3x85 and the glide-avalange value is at least 0.3 xcexc-inch greater than that on untextured surfaces.
There are disadvantages attendant upon laser texturing a glass-ceramic substrate employing a pulsed focused laser light beam. Specifically, the texture comprises discrete dome shaped protrusions having a height no less than about 50 xc3x85. A large heating gradient is required which causes stress around the bumps. It is also difficult to achieve a high bump density. In addition, lithium ion migration causes corrosion. Moreover, the laser power utility is undesirable.
For tribological purposes, i.e., ultra-low glide, low stiction and low wear rate at the head-media-interface, a continuous textured landing zone with a controllable surface roughness is required. Accordingly, there exists a need for magnetic recording media and methodology for manufacturing magnetic recording media comprising a glass-ceramic substrate having a continuous textured landing zone with controllable roughness and a low flying height.
An object of the present invention is a method of manufacturing a magnetic recording medium comprising a glass-ceramic substrate having a continuous textured landing zone with controllable roughness and a low flying height.
Another object of the present invention is a magnetic recording medium comprising a glass-ceramic substrate having a continuous textured landing zone with a low flying height.
Additional objects, advantages and other features of the present invention will be set forth in the description which follows and in part will become apparent to those having ordinary skill in the are upon examination of the following or may be learned from the practice of the present invention. The objects and advantages of the present invention may be realized and obtained as particularly pointed out in the appended claims.
According to the present invention, the foregoing and other objects are achieved in part by a method of manufacturing a magnetic recording medium, the method comprising substantially uniformly heating a zone on a surface glass-ceramic substrate with a continuous wave laser light beam to increase surface roughness.
Another aspect of the present invention is a magnetic recording medium comprising a glass-ceramic substrate having an annular landing zone defined by a substantially uniform roughness comprising recrystallized microcrystals.
Embodiments of the present invention comprise impinging a shaped continuous wave rectangular laser light beam having a flat top intensity profile on a rotating glass-ceramic substrate to substantially uniformly heat an annular zone and air cooling to induce surface roughness comprising crystallized microcrystals, the annular zone comprising a landing zone having an average surface roughness (Ra) of about 6 xc3x85 to about 30 xc3x85, e.g., about 5 xc3x85 to about 20 xc3x85, and an average roughness peak (Rp) of about 20 xc3x85 to about 120 xc3x85. Advantageously, magnetic recording media in accordance with embodiments of the present invention are capable of being employed with a transducer head at a glide height less than about 3 xcexc-in., e.g., about 0.2 to about 0.5 xcexc-in.
Additional objects and advantages of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein embodiments of the present invention are described, simply by way of illustration of the best mode contemplated for carrying out the present invention. As will be realized, the present invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.